The present invention relates to a method for extracting bitumen from bituminous sand.
Hydrocarbons and hydrocarbonaceous oils may be recovered from association with hydrocarbon-containing solids such as tar sands, oil shale and the like, and can be used as substitutes or supplements for petroleum and petroleum derivatives. One key factor in any practical system for solvent extraction of large amounts of hydrocarbons from solids is the economical recovery of solvent from the residual solids. Another important factor is recovering as much of the hydrocarbonaceous material as possible.
One tar sand solvent-extraction process previously proposed involves mixing a solvent with the tar sand and then draining off the resulting mixture of solvent and extracted hydrocarbons (bitumen). After being drained off, bitumen and solvent are then separated by fractionation. The bitumen is normally subjected to further conventional refining. After the bitumen and solvent have been drained from the solids, the solids are treated to remove any adhering solvent by steam stripping. Each extraction and drain stage can include countercurrent washing of the solids with solvent.
In U.S. Pat. No. 3,475,318, it is proposed to solvent-extract tar from tar sands using aliphatic hydrocarbons having 5 to 9 carbon atoms or mixtures of such aliphatics with up to 20% or aromatics having 6 to 9 carbon atoms. The tar sand is broken down into particles of a size between 0.03 and 0.25 inch diameter before solvent extraction. Solvent is passed over a bed of tar sand formed on a filter. The solid and tar are separated from the solvent residue by filtration. After filtration, the solids are stripped of volatiles with steam, which is employed at a rate of 3-21 pounds per 100 pounds of sand for a time of 0.5 to 3 minutes. Solvent is recovered by decantation from the subsequently condensed steam.
In U.S. Pat. Nos. 3,573,195 and 3,573,196 it is proposed to extract bitumen from bituminous sand by mixing the sand with water and hydrocarbon diluent containing dissolved normally gaseous (C.sub.1 -C.sub.3) hydrocarbons, at a temperature of less than 40.degree. F. and then introducing the resulting mixture into a body of water maintained at a temperature above 65.degree. F. The normally gaseous hydrocarbons come out of solution and float the bitumen to the surface of the water for recovery. The hydrocarbon diluent is recovered by decantation from the water.
U.S. Pat. No. 3,875,046 discloses a solvent-extraction process using a single vertically extending extraction vessel. Downwardly flowing particulate tar sand is fluidized by an upwardly flowing liquid mixture of water and hydrocarbon solvent. The hydrocarbon solvent is selected to boil at a temperature below the boiling point of water. Steam is introduced into an intermediate level of the vessel to scour the solvent from the residual sand. Solvent is introduced above the steam introduction point, and water is introduced below the steam introduction point. Solvent condenses on the cooler sand higher up in the bed. The tar and hydrocarbon solvent are separated from water above the top of the tar sand bed by decantation and the solvent phase and water phase are removed. The water introduced into the lower end of the bed contains agglomerated fines. The wet, stripped sand is removed from the bottom of the vessel. The amount of hydrocarbon solvent employed is preferably that sufficient to control the viscosity of the tar recovered. The problem of solvent recovery is discussed. That is, this patent recognizes that a practical process for solvent extraction of hydrocarbon-containing solids necessarily must include some more or less effective means for recovering the organic solvent from the residual solids before the solids are discarded. The more solvent that is lost with the solid residues, the less economical will be a given solvent-extraction process.
Single solvents for bitumen are often overly selective for fractions of bitumen, whereas it is advantageous to extract as much hydrocarbonaceous material as possible from the sand. For example, lighter hydrocarbon solvents tend to extract the lighter bitumen fractions selectively, leaving potentially valuable hydrocarbonaceous materials, such as asphaltines, in the residue.
U.S. Pat. No. 3,117,922 discloses a bitumen recovery operation in which tar sand is first extracted with a higher-boiling hydrocarbon solvent on a moving filter belt and then washing the residual solids with a lower-boiling hydrocarbon solvent. U.S. Pat. No. 3,131,141 discloses contacting tar sand with a gas oil solvent and further contacting the residue with a liquefied, normally gaseous hydrocarbon solvent.